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Date: Tue, 18 May 2021 12:38:46 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
akpm@...ux-foundation.org
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
Jeff Layton <jlayton@...nel.org>
Subject: Re: [PATCH v10 22/33] mm/filemap: Add __folio_lock_or_retry
On 5/11/21 11:47 PM, Matthew Wilcox (Oracle) wrote:
> Convert __lock_page_or_retry() to __folio_lock_or_retry(). This actually
> saves 4 bytes in the only caller of lock_page_or_retry() (due to better
> register allocation) and saves the 20 byte cost of calling page_folio()
> in __folio_lock_or_retry() for a total saving of 24 bytes.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Acked-by: Jeff Layton <jlayton@...nel.org>
> ---
> include/linux/pagemap.h | 9 ++++++---
> mm/filemap.c | 10 ++++------
> mm/memory.c | 8 ++++----
> 3 files changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 41224e4ca8cc..21e394964288 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -640,7 +640,7 @@ static inline bool wake_page_match(struct wait_page_queue *wait_page,
>
> void __folio_lock(struct folio *folio);
> int __folio_lock_killable(struct folio *folio);
> -extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
> +int __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
> unsigned int flags);
> void unlock_page(struct page *page);
> void folio_unlock(struct folio *folio);
> @@ -701,13 +701,16 @@ static inline int lock_page_killable(struct page *page)
> * caller indicated that it can handle a retry.
> *
> * Return value and mmap_lock implications depend on flags; see
> - * __lock_page_or_retry().
> + * __folio_lock_or_retry().
> */
> static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
> unsigned int flags)
> {
> + struct folio *folio;
> might_sleep();
> - return trylock_page(page) || __lock_page_or_retry(page, mm, flags);
> +
> + folio = page_folio(page);
> + return folio_trylock(folio) || __folio_lock_or_retry(folio, mm, flags);
> }
>
> /*
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 67334eb3fd94..28bf50041671 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1623,20 +1623,18 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait)
>
> /*
> * Return values:
> - * 1 - page is locked; mmap_lock is still held.
> - * 0 - page is not locked.
> + * 1 - folio is locked; mmap_lock is still held.
> + * 0 - folio is not locked.
> * mmap_lock has been released (mmap_read_unlock(), unless flags had both
> * FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
> * which case mmap_lock is still held.
> *
> * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
> - * with the page locked and the mmap_lock unperturbed.
> + * with the folio locked and the mmap_lock unperturbed.
> */
> -int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
> +int __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
> unsigned int flags)
> {
> - struct folio *folio = page_folio(page);
> -
> if (fault_flag_allow_retry_first(flags)) {
> /*
> * CAUTION! In this case, mmap_lock is not released
A bit later in this branch, 'page' is accessed, but it no longer exists. And
thus as expected, it doesn't compile. Assuming it's fixed later, but
bisectability etc...
> diff --git a/mm/memory.c b/mm/memory.c
> index 86ba6c1f6821..fc3f50d0702c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4065,7 +4065,7 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
> * We enter with non-exclusive mmap_lock (to exclude vma changes,
> * but allow concurrent faults).
> * The mmap_lock may have been released depending on flags and our
> - * return value. See filemap_fault() and __lock_page_or_retry().
> + * return value. See filemap_fault() and __folio_lock_or_retry().
> * If mmap_lock is released, vma may become invalid (for example
> * by other thread calling munmap()).
> */
> @@ -4307,7 +4307,7 @@ static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
> * concurrent faults).
> *
> * The mmap_lock may have been released depending on flags and our return value.
> - * See filemap_fault() and __lock_page_or_retry().
> + * See filemap_fault() and __folio_lock_or_retry().
> */
> static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
> {
> @@ -4411,7 +4411,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
> * By the time we get here, we already hold the mm semaphore
> *
> * The mmap_lock may have been released depending on flags and our
> - * return value. See filemap_fault() and __lock_page_or_retry().
> + * return value. See filemap_fault() and __folio_lock_or_retry().
> */
> static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> unsigned long address, unsigned int flags)
> @@ -4567,7 +4567,7 @@ static inline void mm_account_fault(struct pt_regs *regs,
> * By the time we get here, we already hold the mm semaphore
> *
> * The mmap_lock may have been released depending on flags and our
> - * return value. See filemap_fault() and __lock_page_or_retry().
> + * return value. See filemap_fault() and __folio_lock_or_retry().
> */
> vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> unsigned int flags, struct pt_regs *regs)
>
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